Enterococcus

Patho/Etiology: Gram-positive cocci in pairs/short chains, catalase-negative, PYR-positive. Part of normal GI/GU flora. Two main species: E. faecalis (more common, more sensitive) and E. faecium (more virulent, more resistant). Notorious for antibiotic resistance. Virulence factors include biofilm formation (adherence to catheters, heart valves) and production of gelatinase and cytolysin.

Clinical Presentation: Primarily a nosocomial pathogen, especially in debilitated, post-operative, or immunocompromised patients with prolonged hospital stays or indwelling devices (e.g., Foley catheters).

• Urinary Tract Infections (UTIs): Most common infection, often catheter-associated.
• Bacteremia/Sepsis: Can follow a UTI or GI/GU procedure.
• Infective Endocarditis (IE): A leading cause of subacute endocarditis, particularly after GI/GU manipulation.
• Intra-abdominal/Biliary Tract Infections: Often polymicrobial, associated with abscesses or biliary procedures.

Diagnosis:

• Culture: Grows in 6.5% NaCl and bile, distinguishing it from non-enterococcal Group D Strep (like S. gallolyticus/bovis).
• Hemolysis: Typically gamma-hemolytic (no hemolysis) on blood agar.
• Urinalysis (for UTI): May show leukocyte esterase but often nitrite-negative (unlike E. coli).

Management/Treatment: Treatment is guided by susceptibility testing due to high resistance rates.

• Ampicillin/Amoxicillin: Drug of choice for susceptible strains, especially E. faecalis.
• Endocarditis: Requires synergistic, bactericidal therapy, typically Ampicillin + Gentamicin (if susceptible to high-level aminoglycosides).
• Vancomycin-Resistant Enterococcus (VRE): A major concern. Resistance mediated by vanA gene, which alters the D-Ala-D-Ala peptidoglycan terminus to D-Ala-D-Lactate.
  • Tx for VRE: Linezolid or Daptomycin. Tigecycline is another option.
• Intrinsic Resistance: Resistant to many cephalosporins, TMP-SMX, and clindamycin.

Key Associations/Complications:

• Nosocomial Infections: Strongly associated with hospital stays, ICU, and long-term care facilities.
• Prior Antibiotic Use: Broad-spectrum antibiotics (especially cephalosporins and vancomycin) select for Enterococcus.
• VRE Transmission: A significant infection control issue, transmitted via hands of healthcare workers. Requires contact precautions.
• Buzzwords: "Grows in 6.5% NaCl," "UTI after GU procedure," "Endocarditis after colonoscopy," "VRE," "D-Ala-D-Lac."